Fiber optic systems are now in common use for transmitting optical communication signals i.e., optical signals modulated to encode desired information. The optical communication signals are transmitted across a network using optical fibers that support substantial transmission capacity with compact fiber bundles. Given the ever-increasing demands for improved signal quality and bandwidth, it is anticipated that the use of fiber optic communications will continue to increase for years to come.
One of the reasons that fiber optic networks have attracted attention in recent years relates to switching advantages. Because the communication signals in fiber optic networks are optical in nature, conventional electronic switching components can be eliminated. Instead, fiber optic communications lines are connected at a switch by carefully aligning the fiber ends of the lines to be connected for direct optical linkage. Such switching has proved advantageous in that switching can be accomplished quickly without unacceptable signal degradation. However, it will be appreciated that there is a continuous desire to increase the speed of operation and reduce signal losses at switch interfaces.
One of the most persistent challenges associated with optical switches is how to quickly and accurately align the fibers that are being connected, i.e., optically interfaced for signal communication therebetween. High speed is required to minimize lag times in the network. Accuracy is required to minimize signal losses. In this regard, it will be appreciated that even slight misalignments of the fiber ends will result in a significant loss of the power of the transmitted optical signal and, potentially, of the information encoded in the signal. Moreover, switch designers are continuously endeavoring to accommodate more fibers in smaller switches. Accordingly, alignment systems remain the focus of much research.
Conventional alignment systems typically employ radiation emitting devices (REDs), such as light or infrared radiation emitting diodes ("LEDs"), lasers or VCSEL lasers for fiber identification and alignment. Fiber identification relates to identifying the fibers that are to be connected for initial targeting and manipulating the switch targeting mechanisms so that the identified fibers are in rough optical alignment. In this regard, it will be appreciated that a typical switch includes a matrix of fiber ends on a first side of the switch and another matrix of fiber ends on a second side. Depending on the switch configuration, these matrices may optically interface directly, or via a folded optical path. In either case, it is generally a function of the switch to be able to optically connect any of the fibers on the first side to any of the fibers on the second side. The fiber identification process allows this connection to be initiated. Thereafter, a fiber alignment process fine tunes the connection to maximize signal transmission or minimize signal losses.
In order to facilitate the targeting and alignment processes, one or more REDs is typically mounted in known spatial relationship to each of the fibers of each matrix, e.g., adjacent to the fiber on the matrix structure. These REDs transmit radiation across the switch interface to the opposing matrix. In addition, an optical receiver is provided in conjunction with each fiber of each matrix. For example, the receiver may be incorporated into a cladding layer of a dual core optical fiber where the central fiber is used for transmission of communication signals. The receiver receives radiation from a RED or REDs of the opposing matrix and provides the received radiation to a detector/feedback system for controlling targeting. In this manner, the REDs can first be used to signal which of the fibers are to be connected. Thereafter, alignment can be optimized by analyzing the signal transmitted from the RED(s) associated with one of the target fibers to the receiver associated with the other and vice versa.
Although such conventional targeting and alignment systems have provided acceptable speed and accuracy, they impose certain limitations in switch designs. First, the REDs and receivers incorporated into the fiber matrices may limit the design of the array or impede array miniaturization. Moreover, the detectors used in such conventional systems generally include a large active area and a correspondingly low signal-to-noise ratio. The dual core fibers used for transmitting and receiving are also very expensive and difficult for switch manufacturers to reliably stock. It would therefore be advantageous to design a fiber optic switch that reduces or eliminates the need for dual core fibers and otherwise addresses limitations of conventional targeting and alignment systems.